The present invention relates in general to hydropneumatic springs and more specifically to a new and improved technique for effecting a hydraulic or pneumatic spring by transferring fluids from one chamber to another axially through a hollow piston support rod.
Conventional hydropneumatic springs provide for the exchange of fluid under pressure between two internal chambers by means of an annular passage or gap defined between concentric tubes, or by a bypass valve and connecting orifice in the piston defining said chambers. Such approaches are complicated, may present safety hazards, and are not entirely satisfactory in operation because of difficulties which exist in maintaining the seals in a lubricated condition.
The present invention overcomes the aforesaid difficulties by transferring the fluid between an upper and lower chamber by means of a hollow tube that serves as the support rod for the piston separating and defining the chambers. As the fluid is transferred a lubricant may be transferred therewith causing an effective lubrication of all seals adjacent the spring fluid.
Toward this end the hydropneumatic spring of the present invention includes a cylindrical casing with upper and lower plugs adjacent each end, the casing containing a fluid under pressure. A hollow piston support rod extends through one of the closed ends of the casing in sealed, slidable and axially guidable relation thereto. The other end of the support rod supports a piston within the cylindrical casing in movable relation with respect to the inner wall thereof. The piston divides the casing into an upper chamber and a lower chamber and includes an axial passageway therethrough which receives the upper end of the hollow piston support rod for selectively establishing communication therethrough between the upper and lower chambers. A valve means selectively opens and closes the path of communication between the upper and lower chambers by passing the fluid from one of the chambers to the other chamber through the hollow piston support rod responsive to axial forces exerted on the hydropneumatic spring which tends to move the cylinder relative to the piston.
More specifically the valve means includes a hollow activating pin open at the bottom and closed at the top extending from a point above the upper plug, through an axial opening in the plug in sliding relation thereto, through the passageway in the piston, into the upper open end of the hollow piston support rod and down into the interior thereof. The activating pin is therefore in constant communication with the interior of the hollow support rod and may be activated from a point outside the casing. The wall of the hollow piston support rod includes an orifice therein below and in close proximity to the piston, thereby establishing communication between the lower chamber and the hollow interior of the piston support rod. The activating pin is selectively axially movable between a locking position and a fluid release position. The wall of the hollow activating pin also includes an orifice therein which is so positioned with respect to the upper plug that the orifice is closed by the upper plug in the locking position and in open free communication with the upper chamber in the fluid release position. Thus fluid communication between the upper and lower chambers is established through the piston support rod and activating pin responsive to axial movement of the activating pin.
Another feature of this invention is a main seal gland, referred to in the industry as a floating gland. Said floating gland is grooved to accept O-rings for sealing against the wall of cylinder and rod. In the past, conventional hydropneumatic springs have utilized annular, composite (elastomer-metal), seals with frustoconical geometries. Such types of seals are difficult and expensive to manufacture to close tolerances, and subject to erratic behavior and failure imposing serious safety hazards. The floating gland permits the use of the highly reliable and inexpensive O-ring seals while at the same time providing for an antifriction surface in contact with the rod.
Another feature of the invention is a main seal floating gland designed in the manner thus far described, but including a special cylinder groove partly chamfered to provide for a relief or relaxation area for the O-ring so that filling of the device is accomplished without the need for delicate and expensive annular frustoconical seals. A more detailed description of this feature occurs in subsequent parts of this specification.
Another feature of the invention is an internal cylinder liner guiding the piston and providing for the proper spacing between the upper plug assembly and the lower main seal and bearing assemblies.
Yet another feature of this invention is a cylinder casing provided with retaining means at both ends, of the groove and ring type, so as to prevent the need for crimping or otherwise cold forming the ends of said cylinder casing in order to retain the elements of the device therein, said forming operations being undesirable due to the need to diminish the diameter of a portion of said cylinder casing and the stresses incurred by said cylinder casing during such operations, all affecting the mechanical properties of said cylinder casing and therefore its ability to safely contain fluid under pressures higher than atmospheric.
Other objects, features, and advantages of the invention will become apparent from reading the detailed description of a preferred embodiment along with the accompanying drawing in which: